INTERPRETATION OF THE COBE FIRAS CMBR SPECTRUM

The cosmic microwave background spectrum measured by the FIRAS instrument on NASA's COBE is indistinguishable from a blackbody, implying stringent limits on energy release in the early universe later than the time t=1 yr after the big bang. We compare the FIRAS data to previous precise measurements of the cosmic microwave background spectrum and find a reasonable agreement. We discuss the implications of the y<2.5x10(-5) and mu<3.3x10(-4) 95% confidence limits found by Mather et al. (1994) on many processes occurring after t=1 yr, such as explosive structure formation, reionization, and dissipation of small-scale density perturbations. We place limits on models with dust plus Population III stars, or evolving populations of IR galaxies, by directly comparing the Mather et al, spectrum to the model predictions.